1. Field of the Invention
This invention relates to a catalyst for the production of unsaturated aldehyde and unsaturated carboxylic acid and a method for the production of unsaturated aldehyde and unsaturated carboxylic acid by the use of this catalyst. More particularly, it relates to a catalyst for producing unsaturated aldehyde and unsaturated carboxylic acid stably at a high yield for a long time by the vapor-phase catalytic oxidation of at least one compound selected from the group consisting of propylene, isobutylene, t-butanol and methyl-t-butyl ether and to a method for the production of unsaturated aldehyde and unsaturated carboxylic acid by the use of this catalyst.
2. Description of the Prior Art
Various improved catalysts have been proposed for the efficient production of unsaturated aldehyde and unsaturated carboxylic acid by the vapor-phase catalytic oxidation reaction of propylene or isobutylene, for example. For example, JP-A-50-13,308 and JP-A-50-47,915 disclose a catalyst having Mo, Bi, Fe, Sb and Ni and at least one element selected among K, Rb and Cs as essential components, and JP-A-64-56,634 discloses a catalyst having Mo, Bi and Fe and at least one element selected among Ni and Co as essential components. As shown from the disclosures mentioned above, most of the proposed catalysts have molybdenum, bismuth and iron as main components thereof.
The problem confronting these catalysts resides in the fact that they are considered to be still deficient not only in the yield of unsaturated aldehyde and unsaturated carboxylic acid but also in the service life of the catalysts. Further, the fact that molybdenum contained in the catalyst is easily sublimed induces an irreversible degradation of catalytic activity. The oxidation reaction mentioned above is an extremely exothermic reaction. With due consideration of the prominent subliming of molybdenum in a catalytic layer, particularly a local abnormal high-temperature zone so called as "hot spot", the use of a catalyst at a high temperature must be avoided to the utmost. A catalyst having a high activity and manifesting the function thereof stably for a long time has been longed for. In particular, in a high-load operation aimed at a high productivity, in the light of the larger amount of accumulated heat in a hot spot in combination with the longer time of using a catalyst at a high temperature because of a more rapid degradation thereof as compared to that in the general reaction, a catalyst which has a high activity and manifests the function thereof stably for a long period is considered to be indispensable.
Solid acids whose magnitudes of acid strength (Ho) (hereinafter referred to simply as "acid strength" or occasionally as "Ho") are not more than -11.93 are generally called as solid super acids as introduced in detail in "SHOKUBAI", Vol. 31, No. 7 (1989), pp. 512 through 518, for example. According to the literature, the super acid is defined as an acid possessing acidity stronger than that of 100% sulfuric acid (Ho.ltoreq.-11.93) and is reported to be usable under more moderate conditions than the ordinary acid catalysts in such reactions as decomposition, isomerization, alkylation, polymerization, acylation, dehydration, and dehydrogenation of hydrocarbon which are referred to as acid catalytic reactions. The fact that this super acid, particularly when combined with a molybdenum-bismuth-iron type catalyst, is effective in inducing the vapor-phase catalytic oxidation reaction for producing unsaturated aldehyde and unsaturated carboxylic acid from propylene and isobutylene, for example, has not been known at all to the art.
One object of this invention, therefore, is to provide a catalyst for producing unsaturated aldehyde and unsaturated carboxylic acid at a high yield.
Another object of this invention is to provide a catalyst for the production of unsaturated aldehyde and unsaturated carboxylic acid which excels in terms of service life and permits the stable operation of the catalytic reaction for a long time.
Still another object of this invention is to provide a catalyst for the production of unsaturated aldehyde and unsaturated carboxylic acid which, even in a high-load operation aimed at high productivity, permits this operation to proceed stably for a long time.
Yet another object of this invention is to provide a method for producing unsaturated aldehyde and unsaturated carboxylic acid efficiently by the use of the catalyst just mentioned above.